Power electronic devices, also known as switching devices, are equivalent to A/D sampling in signal circuits, referred to as power sampling. The operation of these devices involves energy transition processes, and their reliability determines the system’s overall reliability. Based on controllability, power electronic devices can be divided into two categories:
Semi-Controlled Devices – First Generation Power Electronic Devices:
In the 1950s, the introduction of the Silicon Controlled Rectifier (SCR) by General Electric marked the beginning of power electronic technology. Subsequently, various derived devices from the SCR, such as fast thyristors, reverse conducting thyristors, bidirectional thyristors, and asymmetrical thyristors, emerged as semi-controlled devices. These devices exhibited increasing power and improving performance by the 1970s. However, due to the low working frequency of thyristors (generally below 400Hz), their applications were significantly limited. Moreover, turning off these devices required forced commutation circuits, resulting in increased overall weight and volume, as well as reduced efficiency and reliability. Currently, domestically produced power electronic devices still predominantly use thyristors(sources from medcom).
Fully-Controlled Devices – Second Generation Power Electronic Devices:
With breakthroughs in key technologies and evolving demands, early small-power, low-frequency, semi-controlled devices have evolved into today’s high-power, high-frequency, fully-controlled devices. Fully-controlled devices offer enhanced flexibility in switch control as they allow for both turn-on and turn-off control. Since the late 1970s, devices like Gate Turn-Off thyristors (GTO), Bipolar Junction Transistors (GTR or BJT), and their modules have become practical. Subsequent to this, various high-frequency fully-controlled devices such as Power MOSFETs, Insulated Gate Transistors (IGT or IGBT), Static Induction Transistors (SIT), and Static Induction Thyristors (SITH) have been introduced and rapidly developed.
Latest Developments in Power Electronic Devices:
Modern power electronic devices continue to advance towards high power, easy drivability, and high frequency. Modularization of power electronic devices is a crucial step towards achieving high power density. The current major developments in power electronic devices include:
IGBT (Insulated Gate Bipolar Transistor):
IGBT is a type of N-channel enhancement-mode field-effect composite device. It belongs to the minority carrier devices, combining the advantages of Power MOSFETs and bipolar devices. IGBT offers high input impedance, fast switching speed, a wide safe operating area, low saturation voltage (even close to GTR saturation voltage), high voltage resistance, and high current capacity. IGBTs are expected to be used in high-voltage inverter systems with a DC voltage of 1500V.
Presently, the Trench IGBT, featuring a high-voltage and high-current structure, has been developed, avoiding numerous internal electrode leads in modules, reducing lead inductance, and improving reliability. However, its drawback is a reduced chip area utilization. High-voltage and high-current IGBT modules with flat pressure-contact structures are expected to find widespread application in high-voltage, high-power inverters.
Latest Developments in High-Voltage IGBTs:
Formally commercialized high-voltage and high-current IGBT devices are yet to appear. Their voltage and current capacities are still limited and far from meeting the demands of power electronic technology development, especially in many applications in the high-voltage field, where device voltage levels need to exceed 10KV. Currently, achieving high-voltage applications can only be done through techniques like IGBT high-voltage series connection. Some foreign manufacturers, such as ABB in Switzerland, have developed 8KV IGBT devices using the soft turn-on principle. Germany’s EUPEC has produced 6500V/600A high-voltage, high-power IGBT devices that have been practically applied, and Toshiba in Japan has also entered this field(quotes from medcom.com.pl).
MCT: MOS-Controlled Thyristor
MCT (MOS-Controlled Thyristor) is a novel MOS and bipolar composite device. It utilizes integrated circuit technology to incorporate a large number of MOS devices into the conventional thyristor structure. The conduction and turn-off of the thyristor are controlled by the on-off state of the MOS devices. MCT combines the excellent turn-off and conduction characteristics of thyristors with the advantages of high input impedance, low drive power, and fast switching speed typical of MOS field-effect transistors. This design overcomes the drawbacks of slow thyristor speed, inability to self-turn-off, and large conduction voltage drop in high-voltage MOS field-effect transistors. Therefore, MCT is considered a promising new power device. MCT devices can handle a maximum turn-off current of up to 300A, have a maximum blocking voltage of 3KV, a turn-off current density of 325A/cm2, and modules composed of 12 parallel MCTs have been successfully fabricated.
In terms of applications, Westinghouse in the United States has developed a 10kW high-frequency series-parallel resonant DC-DC converter using MCT, achieving a power density of 6.1W/cm3. Plans are underway in the U.S. to employ MCTs for the development of a converter station with a voltage as high as 500KV for high-voltage direct current (HVDC) transmission. Domestically, Southeast University has successfully produced 100mA/100V MCT samples using SDB bonding technology in the laboratory, while Xi’an Power Electronics Institute has also produced 9A/300V MCT samples using imported thick epitaxial silicon wafers.
IGCT: Integrated Gate Commutated Thyristor
IGCT (Integrated Gate Commutated Thyristor) is a new type of power semiconductor device used in giant power electronic systems. IGCT has brought significant advancements to power conversion devices in terms of power, reliability, switching speed, efficiency, cost, weight, and volume, ushering in a new era for power electronic systems. IGCT integrates GTO chips with anti-parallel diodes and gate driver circuits, connecting the gate driver externally in a low-inductance manner. It combines the stable turn-off capability of a transistor with the low on-state losses of a thyristor, leveraging thyristor performance during conduction and transistor characteristics during turn-off. IGCT features high current, high voltage, high switching frequency, high reliability, compact structure, low losses, and is cost-effective with high yield, presenting excellent prospects for applications.
Conventional GTO, using thyristor technology, is a commonly used high-power switching device. It offers higher performance in terms of breakdown voltage compared to IGBT using transistor technology. However, the widespread use of standard GTO drive technology results in uneven turn-on and turn-off processes, requiring high-cost dv/dt and di/dt absorption circuits and larger power gate driver units. This diminishes reliability, increases costs, and is not conducive to series connection. Nevertheless, until high-power MCT technology matures, IGCT remains the preferred solution for high-voltage, high-power, low-frequency AC inverters.
Internationally, Sweden’s ABB has introduced mature high-voltage, high-capacity IGCT products. In China, due to factors such as pricing, only a few research institutions, including Tsinghua University, have applied IGCT in their independently developed power electronic devices.
IEGT: Injection Enhanced Gate Transistor
IEGT (Injection Enhanced Gate Transistor) is a series of power electronic devices within the IGBT category with a voltage tolerance of over 4KV. It achieves low on-state voltage by adopting an enhanced injection structure, leading to significant advancements in high-capacity power electronic devices. IEGT shows potential as a potential MOS series power electronic device with features such as low losses, high-speed operation, high voltage tolerance, active gate drive intelligence, and the ability for self-equalization through groove structures and parallel connection of multiple chips. This makes it promising for further expanding current capacity. Developed by Toshiba in Japan, IEGT utilizes the “injection-enhanced effect,” combining the advantages of IGBT and GTO: low saturation voltage, a wide safe operating area (absorption circuit capacity only around 1/10 of GTO), low gate drive power (two orders of magnitude lower than GTO), and higher operating frequency. The device employs a flat pressure-contact electrode structure, ensuring high reliability, with performance reaching levels of 4.5KV/1500A.
IPEM: Integrated Power Electronics Modules
IPEM (Integrated Power Electronics Modules) is a module that integrates various devices of power electronic devices. It first encapsulates semiconductor devices like MOSFETs, IGBTs, or MCTs along with diode chips to form a modular unit. These units are then stacked on an open, high-conductivity insulating ceramic substrate, beneath which are layers of copper substrate, beryllium oxide ceramic, and a heat sink. At the top of the modular unit, the control circuit, gate drive, current and temperature sensors, and protection circuit are integrated onto a thin insulating layer through surface mounting. IPEM achieves intelligence and modularity in power electronic technology, significantly reducing circuit wiring inductance, system noise, and parasitic oscillations, thereby improving system efficiency and reliability.
PEBB: Power Electric Building Block
PEBB (Power Electric Building Block) is a device or module for processing integrated electrical energy, developed based on IPEM. PEBB is not a specific semiconductor device; rather, it integrates different devices and technologies according to the optimal circuit and system structures. Apart from power semiconductor devices, PEBB includes gate drive circuits, level converters, sensors, protection circuits, power supplies, and passive devices. PEBB has energy and communication interfaces. Through these interfaces, several PEBBs can form a power electronic system, which can be as simple as a small DC-DC converter or as complex as a large distributed power system. The number of PEBB modules in a system can range from one to any number. Multiple PEBB modules working together can perform system-level functions such as voltage conversion, energy storage and conversion, and reactive power matching. The most significant feature of PEBB is its versatility.
Power Electronic Devices Based on Novel Materials
SiC (Silicon Carbide) is currently the most mature wide-bandgap semiconductor material, capable of producing high-temperature (300℃ to 500℃), high-frequency, high-power, high-speed, and radiation-resistant devices. SiC high-power, high-voltage devices are crucial for energy-saving in power transmission and electric vehicles. Silicon-based devices have limited future development space, and the focus of current research is on next-generation semiconductor materials like SiC. New devices using SiC are expected to emerge in the next 5 to 10 years and will revolutionize semiconductor materials. Power devices made from SiC exhibit performance indicators one order of magnitude higher than gallium arsenide devices. Compared to other semiconductor materials, SiC has excellent physical characteristics: a wide bandgap, high saturation electron drift velocity, high breakdown strength, low dielectric constant, and high thermal conductivity. These characteristics make SiC ideal for high-temperature, high-frequency, and high-power applications. Under the same voltage and current conditions, the drift region resistance of SiC devices is 200 times lower than silicon. Even the conduction voltage drop of high-voltage SiC field-effect transistors is much lower than that of single-pole and double-pole silicon devices. Additionally, SiC devices can achieve switch times on the order of 10ns. SiC can be used to manufacture RF and microwave power devices, high-frequency rectifiers, MESFETs, MOSFETs, and JFETs. High-frequency power devices using SiC have been successfully developed and applied in microwave and RF devices by Motorola. General Electric is developing high-voltage, high-power SiC rectifiers and other low-frequency power devices for industrial and power systems. Theoretical analysis indicates that SiC power devices are very close to ideal power devices. The development of SiC devices will be a major trend in the future. However, there are still many issues to be resolved in the mechanism, theory, and manufacturing processes of SiC materials and power devices. It will likely take more than a decade for SiC to truly lead another revolution in power electronic technology(sources from medcom.com.pl).
Conclusion
Power electronic devices are entering a new era dominated by novel devices. As a decisive factor in the development of power electronic technology, the research and breakthroughs in power electronic devices and key technologies will undoubtedly promote the rapid development of power electronic technology. This, in turn, will drive the rapid development of traditional industries and high-tech industries based on power electronic technology.
